1. Field of the Invention
The present invention relates generally to network management systems, and more specifically is directed toward the determination of a root cause of error activity at one or more signal transport levels.
2. Related Art
Telecommunication service providers (e.g., MCI Telecommunications Corporation) provide a wide range of services to their customers. These services range from the transport of a standard 64 kbit/s voice channel (i.e., DS0channel) to the transport of higher rate digital data services (e.g., video). Both voice channels and digital data services are transported over the network via a hierarchy of digital signal transport levels. For example, in a conventional digital signal hierarchy 24 DS0 channels are mapped into a DS1 channel. In turn, 28 DS1 channels are mapped into a DS3 channel.
Routing of these DS1 and DS3 channels within a node of the network is performed by digital cross-connect systems. Digital cross-connect systems typically switch the channels at the DS1 and DS3 signal levels. Transmission of channels between nodes is typically provided via fiber-optic transmission systems. Fiber-optic transmission systems can multiplex a plurality of DS3 channels into a higher rate transmission over a single pair of fibers. In one example, signal formats for the fiber-optic transmission systems are defined by the manufacturer. These proprietary systems are referred to as asynchronous transmission systems.
Alternatively, a fiber-optic transmission system can implement the synchronous optical network (SONET) standard. The SONET standard defines a synchronous transport signal (STS) frame structure that includes overhead bytes and a synchronous payload envelope (SPE). One or more channels (e.g., DS1 and DS3 channels) can be mapped into a SPE. For example, a single DS3 channel can be mapped into a STS-1 frame. Alternatively, 28 DS1 channels can be mapped into virtual tributaries (VTs) within the STS-1 frame.
Various STS-1 frames can be concatenated to produce higher rate SONET signals. For example, a STS-12 signal includes 12 STS-1 frames, while a STS-48 signal includes 48 STS-1 frames. Finally, after an STS signal is converted from electrical to optical, it is known as an optical carrier (OC) signal (e.g., OC-12 and OC-48).
An end-to-end path of a provisioned channel within a network typically traverses a plurality of nodes. This provisioned channel is carried over transmission facilities that operate at various rates in the digital signal hierarchy. For example, a provisioned DS1 channel may exist as part of a DS3, VT1.5, STS-1, STS-12, OC-12, and OC-48 signal along parts of the end-to-end path. This results due to the multiplexing and demultiplexing functions at each of the nodes.
One of the goals of a network management system is to monitor the performance of the provisioned channel. Performance of the provisioned channel can include various measures. One measure is the unavailability of the provisioned channel. Unavailability is generally defined as the amount (or fraction) of time that a channel is not operational. Various causes such as cable cuts can lead to channel downtime. Network responses to channel downtime can include automatic protection switching or various restoration procedures (e.g., digital cross-connect distributed restoration).
Although unavailability is a major performance measure from a customer's standpoint, other performance measures can also be critical. For example, if a customer desires a digital data service for the transmission of financial data, the number of errored seconds or severely errored seconds may be a concern.
In conventional network management systems, performance monitoring is accomplished in piecewise fashion. For example, consider a provisioned channel that traverses an end-to-end path comprising asynchronous transmission systems and SONET transmission systems. Performance monitoring information for these two types of transmission systems is typically maintained in separate databases. Moreover, the various types of transmission systems may be provided by multiple vendors. Each of these vendors may define their own separate performance monitoring process. For example, the vendor-controlled process may define the types of data that are retrieved from or reported by the individual network elements.
In this environment, comprehensive performance monitoring analysis is difficult to accomplish. What is needed is a network management system that can monitor provisioned channels at various points of the end-to-end path and identify the root cause of problems that lead to observable error activity. This capability allows a service provider to efficiently resolve problems that lead to degradation of network performance.